Disk devices, such as hard disk drives (HDDs) generally include a magnetic disk as a recording medium and a slider facing the magnetic disk. In such a HDD, the slider includes at least a head portion having a reading head (or element) and a recording head (or element) and a heater element, and floats over the rotating magnetic disk. Regarding reading and writing of data on the magnetic disk, there are well-known techniques for improving magnetic characteristics between the head portion disposed in the slider and the magnetic disk. Specifically, there is a technique for controlling floating of the slider over the magnetic disk so as to shorten a distance between the head portion and the magnetic disk (i.e., to lower a fly height of the head portion with respect to the magnetic disk. This technique may also be referred to as dynamic fly height (DFH) control, or thermal fly height control (TFC) in some cases. In some cases, a preheating process is executed, in which the heater element is heated at a point in time prior to a point in time at which the head portion passes a target position for reading or writing in the floating control. Execution of the preheating processing enables a desired fly height of the head portion to be obtained at the point in time at which the head portion passes the target position.